This invention relates to a method of creating pulses from a copper vapor laser of less than 10 nsec FWHM (Full Width Half Maximum) duration of use in such applications as femtosecond pulse amplification, frequency doubling, coastal mapping, underwater object detection, and the like.
The output pulse from a standard copper vapor laser generally includes a series of peaks, the number of which depends upon the resonator design. This pulse shape is not ideal for any of the applications mentioned above. For certain applications, it is desirable to modify the pulse temporal shape to produce a single peak of duration less than 10 nanoseconds (nsec.). One technique for doing this is to increase the laser cavity length. This effectively removes some of the peaks at the end of the pulse, but fails to remove the initial peak. In addition, it does not increase the power in the main peak. Another technique incorporates a cavity dumper or Q-switch in the laser cavity. This is not practical for copper vapor lasers because of the large beam diameters (typically greater than 1 inch). Most Q-switches with fast enough response have much smaller clear apertures, and thus have not been successfully used on copper vapor lasers.
The copper vapor laser, because of its high gain, is unpolarized. Typically lasers utilize Brewster angle windows to polarize the beam. These windows have high loss in one polarization and low loss in the other. The high loss polarization fails to support laser action because the gain is less than the loss. In copper vapor lasers, the gain is much higher than the loss and thus laser action can be supported in both polarizations. Consequently windows are not installed at Brewsters angle, but rather at a angle near normal incidence.